Attempts are being made to downsize electronic equipment such as cellular phones, personal digital assistants and the like. In addition to the downsizing of the electronic equipment, attempts are also being made to use a fuel cell for the power source of the electronic equipment. The fuel cell can generate electricity by merely supplying fuel and air and can continuously generate electricity by changing and replenishing the fuel only. Therefore, if the fuel cell can be downsized, it is effective as a power source for compact electronic equipment.
As the fuel cell, a direct methanol fuel cell (hereinafter referred to as DMFC) attracts attention. The DMFC is classified according to a liquid fuel supplying method, and the supplying method includes an active method such as a gas supply type, a liquid supply type or the like and a passive method such as an inside vaporization type which supplies the liquid fuel from a fuel storing unit to a fuel electrode by vaporizing in the cell. Between them, the passive method is advantageous for downsizing of the DMFC.
It is usual that the fuel cell is activated and put into a steady operation state before it is connected to a load.
It was found that the startup of the DMFC becomes instable occasionally due to an external environment, and particularly a temperature. That is, the fuel tank inner pressure increases in a high temperature environment, and the fuel supply amount from the fuel tank to the DMFC increases easily. On the other hand, the fuel tank inner pressure decreases in a low temperature environment, and the fuel supply amount from the fuel tank to the DMFC decreases easily. Therefore, the supply of the fuel becomes excessive in the high temperature environment, and the DMFC temperature rises sharply, resulting in possibility of an occurrence of overshooting. On the other hand, the supply of the fuel becomes insufficient in the low temperature environment, and it might take time to startup the DMFC.
To remedy the instable startup of the DMFC due to the influence of the outside temperature, it is considered to measure the outside temperature and to control the fuel supply depending on the outside temperature.
But, it is not preferable to dispose a sensor for measuring the outside temperature because the DMFC will have a complex equipment structure. The temperature of the DMFC itself can be measured by a temperature sensor disposed within the DMFC. On the other hand, the measurement of an outside temperature of the DMFC requires the temperature sensor disposed outside the DMFC, and the equipment structure of the DMFC becomes complex.
In view of the above, it is desired to have a fuel cell startup method which has excellent robustness with respect to an outside temperature and does not require a sensor for measuring the outside temperature.